The present invention relates in general to active bolsters for occupant crash protection in automotive vehicles, and, more specifically, to an active bolster with an inflatable bladder formed by a plastic panel with pleats that unfold during inflation so that the bolster moves evenly into position for cushioning an impacting body.
An active bolster is a vehicle occupant protection device with a gas-inflatable bladder to absorb impacts and reduce trauma to occupants during a crash. As opposed to deployable air bag cushions that emerge from behind various openings upon inflation, active bolsters use the interior trim surface itself to expand at the beginning of a crash event for absorbing the impact and dissipating energy through the action of an inflation gas. U.S. Pat. No. 8,205,909, issued Jun. 26, 2012, incorporated herein by reference, discloses an active knee bolster integrated into a glove box door that is light weight and visually attractive. Pending U.S. application Ser. No. 13/089,401, filed Apr. 19, 2011, also incorporated herein by reference, discloses a typical structure wherein an active bolster includes a front wall or panel that faces a vehicle occupant attached to a base wall or panel along a sealed periphery. One or both of the walls is deformable in order to provide an inflatable bladder. For example, the base wall may have a pleated (i.e., accordion-like) region that straightens out during inflation. The walls are initially spaced apart by a small amount when in their pre-deployment, non-inflated condition. This allows ingress of the inflation gas in a manner that achieves even inflation across the panel.
The front and base walls of a typical active bolster are comprised of molded thermoplastics such as polyethylene, polyolefin, or PVC. They are typically injection molded but could also be blow molded. When formed separately, the front and base walls must be hermetically joined around their periphery in order to form the inflatable bladder. The joint must be strong to resist separation as a result of the high pressures during inflation.
Expansion of an active bolster must be consistent in order to achieve a reliable placement in a position for optimally receiving the body of an impacting passenger. For example, with an active knee bolster mounted in a glove box door, an even expansion is desirable in order to capture both knees of the passenger as close to the same time as possible. Due to the need for fast deployment, a relatively high pressure, high volume inflator is used. The high forces from the inflation gas often lead to an uneven expansion of the bolster which may vary from one unit to the next. Besides a lack of control over the shape or positioning of the bolster during expansion, an uneven expansion can involve a portion of the bladder expanding at a much greater rate than other portions, which results in an increase in stress applied to the hermetic seal at that portion. Consequently, the weld between the walls of the bladder may be more likely to fail during deployment.